This representative point is usually the centre of mass 11 Describing

# This representative point is usually the centre of

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– (This representative point is usually the centre of mass.) 11 Describing motion(1.Motion Diagrams, 2.Graphs, 3. Equations); Position and displacement; Velocity; Acceleration; Free Fall Reference Frames : – The motion of a physical object is always described within a certain frame of reference. Your coordinate axes are defined with respect to a certain origin. Laboratory frame (often: x pos. to the left, y pos. up.) Starting positions and times are often set to zero: x i = x 0 = 0 m and t i = t 0 = 0 s. – Choice of reference frames important for accelerating objects (e.g., elevators, trains,...) or objects moving relative to each other. 12 Describing motion(1.Motion Diagrams,2.Graphs, 3.Equations ); Position and displacement; Velocity; Acceleration; Free Fall 3. Equations: Equations involving quantities with well defined meanings such as velocity, acceleration, displacement, mass… – Equations are precise and allow to predict the outcome of experiments. 5 13 Describing motion(1.Motion Diagrams,2.Graphs, 3.Equations ); Position and displacement; Velocity; Acceleration; Free Fall Displacement: Vector pointing from the initial to the final position: - vector (“Net distance traveled with direction”.) Average Speed : Distance traveled in time t. v = distance/time - scalar Average Velocity : v = displacement/time - vector • Acceleration : a = velocity/time - vector i f r r r = Δ 14 Describing motion(1.Motion Diagrams,2.Graphs, 3.Equations ); Position and displacement; Velocity; Acceleration; Free Fall Vectors and Scalars : •When a physical quantity is described by a single number we call it a scalar. •In contrast a vector has both a magnitude and direction in space. •Vector notation •Magnitude of vector or A A r A r 15 Describing motion(1.Motion Diagrams,2.Graphs,3.Equations); Position and displacement ; Velocity; Acceleration; Free Fall Mathematically, we describe the motion of an object as follows: – Call the initial position x i (at a time t i ) – Call the final position x f (at a later time t f > t i ) – The displacement is given by Δ x = x f – x i You may obtain a negative displacement such as Δ x = - 1.7 m. What does it mean? Important: Displacement is not equal to the distance traveled. Why? 6 16 Question A ball is tossed vertically upwards and after reaching a max. height of 3.0 m, it falls to the floor. The ball comes to rest exactly 1.0 m below its starting position. If x is positive upwards, what is the displacement of the ball? A) 1.0 m B) 7.0 m C) 3.0 m D) - 1.0 m E) - 7.0 m 17 Question A ball is tossed vertically upwards and after reaching a max. height of 3.0 m, it falls to the floor. The ball comes to rest exactly 1.0 m below its starting position. What is the total distance traveled?  #### You've reached the end of your free preview.

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• Spring '09
• Lioudmila
• Acceleration, Velocity, Vavg
• • • 